Commonly called "dumbcane," the dieffenbachia (Dieffenbachia seguine) is a tropical evergreen perennial native to Brazil. All parts of this attractive plant contain toxins that will cause stomach upset if eaten, or a skin rash if sap is oozed from the stem or leaves. It is not tolerant of frost but can be grown outdoors year round in tropical gardens in U.S. Department of Agriculture hardiness zones 11 and warmer. Otherwise grow it as a houseplant. Many varieties of dumbcane exist, all with large, paddle-like leaves with variously patterned and variegated colorations.
Place the dumbcane plant in a warm, draft-free location in the home where it will receive bright indirect light. Avoid a northern window as the light intensity is too low, especially from fall to spring. Situate the plant's container just out of the reach of direct sun rays that come through the window. From late fall to early spring, allow the weaker sun rays to reach all the leaves to prevent the plant from getting leggy or aborting leaves.
Water the soil occasionally so that it remains between slightly dry to moist. Allow municipal tap water to rest for a couple hours in the watering can so chlorine gas escapes from the water. Never over-water the soil so that it is soggy or saturated. Make sure there are drainage holes in the container bottom so that the roots do not rest in water. In the winter months, reduce watering so that the soil is drier between the less frequent waterings.
Apply a balanced formula of liquid houseplant fertilizer according to directions on the product label only during the spring and summer months. Fertilize the dumbcane only once a month as part of a watering event. Do not fertilize the plant from fall to spring.
Mist the foliage of the plant daily with a spray bottle with room-temperature water in the summer months. Increased ambient humidity in summer when the plant is actively growing prevents leaf edges from browning.
Increase ambient humidity and ensure excellent drainage of water from the plant container by setting it in a gravel-filled tray basin. Use a large pot basin that is filled with 2 inches of pea gravel and place the dumbcane pot on top of it. Fill the basin with 1-inch of water so that it evaporates and naturally increases the humidity around the plant. Make sure the plant roots never sit in an over-filled gravel tray as it will cause root rot.